The long-distance transport of visible light through a building can use large mirror-lined ducts, or smaller solid light guides which exploit total internal reflection. Mirror-lined ducts include advantages of large cross-sectional area and large numerical aperture (enabling larger fluxes with less concentration), a robust and clear propagation medium (i.e., air) that leads to both lower attenuation and longer lifetimes, and a potentially lower weight per unit of light flux transported. Solid light guides include the advantage of configuration flexibility, which can result in relatively tight bends with low light loss. While the advantages of mirror-lined ducts may appear overwhelming, solid light guides are nevertheless frequently selected because of the practical value of assembling light conduits in much the same fashion as plumbing. Regardless of the technique used to transport light effectively, a practical and efficient daylight collector that is adapted to the transport system is needed.
Fiber optics based daylighting systems collecting light outside a building and transporting it over long distance through optical fiber cables to the interior have been described e.g. in U.S. Pat. Nos. 4,389,085 and 5,581,447. These systems can collect and concentrate large quantities of direct sunlight with a high concentration factor for coupling into a fiber optic cable. Their sun acceptance angle is however very small and they need thus bi-axially sun tracking mechanic devices which are expensive to produce, require intense maintenance in use, and are very bulky which makes integration into the facade of a building extremely challenging.
In DE 3604269, U.S. Pat. Nos. 5,709,456, and 6,059,438 a fiber optic system that uses a static (non sun-tracking) collector based on light absorbing and re-emitting dyes is proposed. Such a system can be flat and thus easily integrated into the facade or the roof of a building. It suffers however under very low optical collection efficiency, a low light concentration factor, and a non-natural light spectrum.
US patent application US 2010/0172147 describes another type of fiber optic system consisting of a static collector with macroscopic prism array modules to collect light and coupling it into a solid light pipe for transport into a building. Patent application WO 2015/098209 describes yet another fiber optic system based on a flat multilayer micro-optic prism film collector design. DE 3522717 describes a fiber optic system with a flat lens based static concentrator element.
All these static collector systems are flat and can in principle easily be integrated into the facade of a building or its roof. They do however not allow a high light concentration factor and a large amount of optical fiber (light pipe) is thus required to transport the light over long distances into the building, which makes the systems extremely expensive and heavy.
Daylighting systems based on mirror lined duct light transport elements are well known. Vertical light tubes for light transport from the roof to the upper floors of a building are described e.g. in U.S. Pat. No. 8,955,269, WO 2011/022274, US 2014/0160570, or EP 1306606. Systems of this class are of only minor interest for multistory office buildings, where distances from the roof to the offices are mostly too long to provide the required light intensity of 500 lx in the central working region (DIN EN 12464-1, office illumination). They are thus limited in their light transport distance to about 5 m or do require a very large cross-section area for transport of light over longer distances, thus occupying a large proportion of the available building volume. For higher light collection efficiency, the systems often comprise a dome covering the light transport duct which may comprise additional optical structures such as Fresnel structures or laser cut panels (LCP). The cover is thus bulky and does make integration of the system into the building envelope challenging.
Horizontal light tubes for building illumination with daylight from the facade have been suggested in CN 102305380 and WO 1998/028645, a system combined with laser cut panels as collector (LCP) was described by V. Garcia Hansen and I. Edmonds in ‘Natural illumination of deep-plan office buildings: light pipe strategies. In: ISES Solar World Congress 2003, 14-19 Jun. 2003, Göteborg, Sweden’ and CN203162829, and another system with CPC type collector elements is described by D. Vázquez-Molini et al. (ADASY, Active Daylighting System; Proc. of SPIE Vol. 7410, 74100H). All these systems do either not allow to collect daylight from an area larger than the cross-section of the mirror lined duct and/or do have bulky extensions protruding from the facade of the building. This makes architectural integration challenging and/or requires presence of expensive optical elements.
A horizontal light tube system with a daylight collector element that allows collecting light from a substantially larger area then the cross-section of the mirror lined duct is proposed in KR 100384277. The collector comprises a condensing portion formed by a frame and a Fresnel lens, and a light change portion formed by two prism lenses. The second prism lens is optically connected to a mirror lined duct. The collector device of this system is however very bulky and can thus not be easily integrated into the facade or roof of a building.
A daylighting system combining a protruding flat collector element comprising macro-optical and mirror structures with a mirror lined duct is proposed in JP 2014/209423 and JP 2014/209424 and JP 2016/048618.
All state of the art daylighting systems described above have the disadvantage of low solar acceptance angle resulting in the need for expensive mechanical tracking systems, and/or need for expensive optical fiber cables for transport of daylight over long distances, and/or bulky collector elements making integration into the building envelope a challenge, and/or need for expensive optical elements, and/or limited optical efficiency. Where used to introduce light from the side of the façade, such devices not only introduce aesthetical breaks into the facade, but also interrupt the building envelope and its thermal shielding.